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Old 10-03-2009, 02:34 PM   #1
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Default Help with school project

Hey,
I am a mechanical engineering student and we have a class project to build and design an electric rc car. We have to use solidworks to design the car and then use our cnc machine to create the parts. We then race them. My question is, is it better to have a belt driven car, or a car that uses a bunch of reduction gears. I am a nitro off roader so i dont know much about the set up of an electric on road car. The motor we have to use isn't very power full and it runs at a constant speed of 2300 rpms. I have to reduce this a bit in order to get the tires to actually grip the ground. We also have to use an electric clutch to engage the motor, the motor will only power the rear wheels, so i was thinking it might be easier to use a series of belts versus having to worry about gear mesh on a bunch of gears. any advice you guys could give me would be great. thank you for your time.
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Old 10-03-2009, 06:30 PM   #2
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2300 is not enough. My 10.5 turn will do 30000 rpm easy. A slow 21.5 turn can do 15000-20000 rpm. You should go to a onroad race and speck to the drivers. With Electric there is no real transmission. Gearing comes from the diffs and spur and pinion gear. Some cars to look at would be the TC5R and Xray T2 009, and TC4.
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Old 10-03-2009, 07:47 PM   #3
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I know 2300rpms is nothing but its what the school is supplying, I dont want to spend money on buying a new motor if i can get one for free and i know everyone else will be running this motor. do you think that with an engine that is this weak i might be able to connected it directly to the rear driveshaft with a belt system?
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Old 10-03-2009, 07:51 PM   #4
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sounds like you might want to do a car liek this http://www.redrc.net/wp-content/uplo...cgenx235-2.jpg

direct drive. you wont lose nearly as much power as using a 4wd belt or shaft transmission. only problem is you either need wider tires in the rear to compensate for having no front steering, or drive very carefully
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Old 10-03-2009, 07:54 PM   #5
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Are you going for a 2wd pan car or a 4wd touring car? By the way a carbon fiber chassis pan car would be best. It very light and with such a low power motor its your best bet. Look at the 12R5.1 Factory Team.
http://67.199.85.166/ae/12r5.1/12r5.1_home.php
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Old 10-03-2009, 07:59 PM   #6
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Another car to look at.
http://www.teamcrc.com/crc/modules.p...rticle&sid=101
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Old 10-04-2009, 01:08 PM   #7
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Quote:
Originally Posted by fievel View Post
have to use isn't very power full and it runs at a constant speed of 2300 rpms. I have to reduce this a bit in order to get the tires to actually grip the ground. We also have to use an electric clutch to engage the motor, the motor will only power the rear wheels
Is that 2300 rpm at a certain voltage? That sounds like a rating in rpm/volt to me. What is your power source? Hobby shops, junked printers, and vcrs give nearly an unlimited choices in gears and belts to build with. Do you have the specs on the surfaces you have to race on? The engineering competitions vary in the requirements from just a flat surface, to carpet, slalom, dirt etc. That will determine the design of your car.
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Old 10-04-2009, 07:14 PM   #8
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First of all, how big is that motor? It may be 2300rpm but it may also have as much torque to pull a truck.
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Old 10-04-2009, 08:30 PM   #9
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Quote:
Originally Posted by cyanyde View Post
First of all, how big is that motor? It may be 2300rpm but it may also have as much torque to pull a truck.
Like gacjr0 and cyanyde said, not nearly enough information in general for anyone to help. Give us the rundown.
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Old 10-04-2009, 08:41 PM   #10
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Quote:
Originally Posted by fievel View Post
I know 2300rpms is nothing but its what the school is supplying, I dont want to spend money on buying a new motor if i can get one for free and i know everyone else will be running this motor. do you think that with an engine that is this weak i might be able to connected it directly to the rear driveshaft with a belt system?
What are the class requirements? Direct Drive with Pinion and spur gear with the motor that is spec'd should be the most effecient,,,,, Belt drive, not so much. So, what is your Prof looking for?
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Old 10-08-2009, 04:21 PM   #11
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Let's say everyone is using a spec battery and motor. Then everyone has about the same "power to weight" ratio in the basic power plant. If this is a brush motor (I suspect), then we can get into that with some battery and motor measurements, if you wish. Set that aside for now ...

In terms of superior acceleration, you want to have a better power to weight ratio, so make your car lighter. You want to have less rotational inertial in the driveline, so belts may be better than gears, however, a direct drive pinion/spur is probably as light and efficient as a similar belt drive.

For better cornering power you want wide tires with good grip, a short wheel base and more track width, keep the center of gravity low, keep heavy components near the center of the car to improve the yaw moment of inertia. For stability in high speed straights you need a longer wheel base which adversely affects some of the cornering characteristics.

What scale is this car? What dimensions are the race course? These issues will effect your choice of gear ratio based on the trade-off between punch and speed for a single speed car. As the guys said, we need more information.
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Old 10-08-2009, 06:03 PM   #12
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look up an old school DELTA 12th scale or 10th scale pan car.
it would be cake to build most of it.

Are you designing and building everything?
are you building your own shocks? if so look into using a foam dampner instead of a fluid filled shock.


what are you available materials?
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